Compositions including nanoparticles having a rutile-like crystalline phase, and methods of making the same

ABSTRACT

Compositions include nanometer-sized particles having a mixed oxide of titanium and antimony are characterized by rutile-like crystal phases.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/990,604, filed Nov. 21, 2001, now pending, the disclosure of which isherein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to nanometer-sized particles comprising oxides oftitanium and antimony, and in particular, to methods of making suchparticles, and compositions and articles containing same.

BACKGROUND OF THE INVENTION

Nanocomposite materials, that is, materials having homogenouslydispersed inorganic nanoparticles in an organic binder, have been usedas protective transparent coatings for various applications. Suchmaterials may have improved abrasion resistance and/or opticalproperties (e.g., refractive index) as compared to coatings of thecorresponding organic binder not having inorganic nanoparticlesdispersed therein.

Nanocomposite materials containing various inorganic nanoparticles, suchas titania (i.e., titanium dioxide) nanoparticles, have been described.Titania occurs in at least three crystal forms: anatase, brookite, andrutile. Of these, the rutile form has the greatest density, hardness,and refractive index.

Major problems with preparing titanium oxide sols, and particularlytitanium oxide sols having the rutile crystalline phase may include:long process times, the need to use additional stabilizing counterions(e.g., chloride, nitrate, etc.) that must be laboriously removed priorto use in applications such as organic protective films, extreme pHvalues, and/or limited stability.

It would be desirable to have quick and easy methods for preparingstable colloidal dispersions of inorganic particles containing titanium,wherein the particles have properties at least comparable to the rutileform of titania. It would also be desirable to homogeneously incorporatesuch particles into an organic binder to provide high index ofrefraction abrasion resistant coatings.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a composition comprising aplurality of Ti/Sb mixed oxide nanoparticles in the form of an aqueouscolloidal dispersion, wherein the Ti/Sb mixed oxide nanoparticlescomprise a rutile-like crystalline phase.

In some embodiments the nanoparticles have at least one organic moietybound to the nanoparticle surface.

In another aspect, the invention provides a method for preparing anaqueous colloidal dispersion of Ti/Sb mixed oxide nanoparticlescomprising the steps of:

-   -   a) providing an aqueous titania precursor;    -   b) providing an aqueous antimony oxide precursor;    -   c) combining with mixing both aqueous precursors; and    -   d) hydrothermally processing the mixture;    -   wherein the weight ratio of titanium to antimony is in the range        of from about 0.14 to about 11.3.

In some embodiments, the method further comprises the step of modifyingthe surface of the nanoparticles.

Colloidal dispersions prepared according to the invention typically arehighly stable.

In another aspect, the invention provides a composition comprisingagglomerated nanoparticles, wherein the agglomerated nanoparticlescomprise Ti/Sb mixed oxide nanoparticles comprising a rutile-likecrystalline phase.

In some embodiments, the agglomerated nanoparticles are redispersibleinto a liquid vehicle.

In another aspect, the invention provides a nanocomposite precursorcomprising a plurality of nanoparticles homogeneously dispersed in anorganic binder precursor, wherein the nanoparticles comprise Ti/Sb mixedoxide nanoparticles containing a rutile-like crystalline phase.

In another aspect, the invention provides a nanocomposite comprising aplurality of nanoparticles dispersed in an organic binder, wherein thenanoparticles comprise Ti/Sb mixed oxide nanoparticles containing arutile-like crystalline phase.

In some embodiments, the nanoparticles have at least one organic moietybound to the nanoparticle surface.

In some embodiments, nanocomposites according to the invention may besupported on a substrate.

Nanocomposites according to the invention are well suited for use asprotective coatings, and may have a high refractive index.

As used herein, the following definitions apply:

-   -   “aqueous titania precursor” refers to an aqueous titanium        containing composition that may be converted to titania by one        or more of heating, evaporation, precipitation, pH adjustment,        and combinations thereof;    -   “aqueous antimony oxide precursor” refers to an aqueous antimony        containing composition that may be converted to antimony oxide        by one or more of heating, evaporation, precipitation, pH        adjustment, and combinations thereof;    -   “hydrothermal processing” means heating in aqueous media, in a        closed vessel, to a temperature above the normal boiling point        of water;    -   “nanoparticle” means a particle having a maximum particle        diameter of less than 500 nanometers;    -   “rutile-like” means having a tetragonal crystal structure and a        space group of P4₂/mnm (#136);    -   “organic moiety” means an organic group, ion, or molecule; and

“mixed oxide” means an intimate mixture of titanium and antimony oxides.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a composite article according to theinvention.

FIG. 2 is a schematic representation of a reaction system useful forpreparing Ti/Sb mixed oxide nanoparticles according to the presentinvention.

FIG. 3 is a cross-sectional view of one embodiment of a pulse dampeneruseful in practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In its various aspects, the invention concerns nanoparticles comprisinga mixed oxide of titanium and antimony (hereinafter abbreviated Ti/Sbmixed oxide), wherein at least a portion of the Ti/Sb mixed oxide has arutile-like crystalline phase.

Nanoparticles

Nanoparticles of the invention comprise Ti/Sb mixed oxide. Typically,the weight ratio of titanium to antimony in the nanoparticles is in therange of about 0.14 to about 11.30, desirably in the range of from about0.22 to about 5.02, and more desirably in the range of from about 0.42to about 2.93.

Ti/Sb mixed oxide nanoparticles according to the invention desirablycomprise a rutile-like crystalline phase. The rutile-like crystallinephase may co-exist with other crystalline phases within individual Ti/Sbmixed oxide nanoparticles. Individual nanoparticles may comprise up to100 weight percent of the rutile-like crystalline phase. Ensembles ofTi/Sb mixed oxide nanoparticles (i.e., all Ti/Sb mixed oxidenanoparticles taken as a whole) will typically comprise nanoparticleshaving a variety of sizes, elemental compositions, and crystallinephases. The term “ensemble average” of a parameter, as used herein,refers to the average value of that parameter across the entire ensemblebeing referred to. Thus, the term refers to a property of the bulk, notnecessarily reflective of that property in each individual member of theensemble.

Desirably, the ensemble average rutile-like crystalline phase content ofTi/Sb mixed oxide nanoparticles is at least about 20 weight percent,more desirably at least about 40 weight percent, more desirably at leastabout 60 weight percent, and even more desirably at least about 80weight percent based on the total weight of Ti/Sb.

In some applications, it may be desirable that substantially all of theTi/Sb mixed oxide nanoparticles contain a rutile-like crystalline phase.

Desirably, as measured by X-Ray Diffraction analysis (i.e., XRD, asdescribed hereinbelow), the ensemble average relative intensity ofrutile-like crystalline phase as compared to anatase, for Ti/Sb mixedoxide nanoparticles of the invention, is greater than about 1:10.Further, it may also be desirable that the relative intensity of anyanatase or antimony oxide maxima observed by XRD have a relativeintensity of less that 1 percent, more desirably less than 0.1 percent,where the relative intensity of the greatest diffraction maximum of therutile-like phase is defined to be 100 percent.

Typically, the Ti/Sb mixed oxide nanoparticles are free of additionalmetallic elements, although for some particular applications it may bedesirable to add additional elements (including silicon). If additionalmetallic elements are present, they are desirably in an amount of lessthan about 0.1 moles per mole of titanium present in the ensembleaverage of Ti/Sb mixed oxide nanoparticles. Exemplary additionalmetallic elements include the rare earth elements.

Ti/Sb mixed oxide nanoparticles of the invention typically have anensemble average particle size of less than about 500 nanometers, moredesirably less than about 100 nanometers, and still more desirably lessthan about 40 nanometers, especially when the nanoparticles are to beincorporated into a transparent coating.

In some embodiments, Ti/Sb mixed oxide nanoparticles may be combinedwith additional nanoparticles having a different elemental composition(e.g., silica, zirconia, alumina, titania, antimony pentoxide).Desirably, such additional nanoparticles, if present, have an averageparticle size comparable to that of the Ti/Sb mixed oxide nanoparticles.Such nanoparticles may be commercially obtained, for example, from NalcoChemical Co. (Naperville, Ill.) or Nyacol Nano Technologies, Inc.(Ashland, Mass.). Exemplary additional nanoparticles are also describedin U.S. Pat. Nos. 5,037,579; 6,261,700; and 6,261,700; which disclosuresare incorporated herein by reference.

In some embodiments of the invention, the nanoparticles are selectedsuch that colloids and nanocomposites are free from a degree of particleagglomeration or coagulation that would interfere with the desiredproperties of the composition. Desirably, individual, unassociated(i.e., non-agglomerated and non-coagulated) particles are dispersedthroughout the composition. In these embodiments, the particlesdesirably do not irreversibly associate (for example, by covalentlybonding and/or hydrogen bonding) with each other.

In other embodiments, such as in the preparation of thin films, it maybe desirable for the nanoparticles to irreversibly agglomerate,especially when employed without a dispersing medium (e.g., liquidvehicle or binder).

Nanoparticles may be present in colloidal dispersions of the inventionin an amount of up to 30 percent, or more. The amount may vary withdensity and surface characteristics of the nanoparticle. Desirably,nanoparticles are present in an amount of from about 1 to about 25weight percent, more desirably from about 10 to about 20 weight percent,of the colloidal dispersion.

Depending on the application, the pH of colloidal dispersions of theinvention may be any value, but typically range from about 4 to about 9,desirably from about 5 to about 8.

Colloidal dispersions of the invention are typically prepared as adispersion of nanoparticles in an aqueous vehicle. The aqueous vehiclecomprises water, typically as the predominant ingredient, and maycontain organic solvents (especially solvents that may be present in thetitania or antimony oxide precursors). Solvent may be added prior to, ormore desirably following, hydrothermal processing. Exemplary organicsolvents include alcohols, ethers, and/or ketones having from 4 to 12carbon atoms. One such desirable solvent is 1-methoxy-2-propanol.

Solvents used in the present invention, if present, are chosen based onvolatility and compatibility with the aqueous titania and antimony oxideprecursors, binder precursor, and/or binder, depending on the point atwhich they may be added.

Nanocomposites

Nanoparticles according to the invention may be incorporated in a binderto form a nanocomposite. The nanoparticles may be either directlyincorporated into the binder, or incorporated into a binder precursorthat is subsequently cured to form a binder. Desirably, nanoparticlesare present in the nanocomposite in an amount of at least 30 weightpercent based on the total weight of the nanocomposite.

Compatibility of inorganic nanoparticles with organic binders istypically achieved by appropriate treatment of the inorganic particleswith a coupling agent.

Prior to incorporation into either a binder or binder precursor,nanoparticles employed in practice of the present invention aretypically surface-modified, which may be achieved by attachingsurface-modifying agent(s) to the particle surface. Surface-modifyingagent(s) attached to the surface of the particle can modify the surfacecharacteristics of the particles to achieve a variety of propertiesincluding, for example, to increase the compatibility of the particleswith the components of the composition, to facilitate dispersion of theparticles in the composition (either from isolated or colloidal form),and to enhance optical clarity of the composition and combinationsthereof. The particles can also be surface-modified to include surfacegroups capable of associating with other components of the composition.When the composition is polymerized, for example, the surface groups canassociate with at least one component of the composition to become partof the polymer network. Preferably, the surface groups are capable ofassociating with the first monomer, the second monomer, or a combinationthereof. Preferably, the particles are surface-modified to include acombination of surface groups capable of providing compositions havingdesired dispersion, clarity, adhesive, and rheological properties.

Schematically, surface-modifying agents can be represented by theformula A-B where the A group is capable of attaching to the surface ofthe particle, and where the B group is a compatibilizing group that maybe reactive or non-reactive with the components of the composition.Compatibilizing groups B that impart polar character to the particlesinclude, for example, polyethers. Compatibilizing groups B that impartnon-polar character to the particles include, for example, hydrocarbons.

Exemplary suitable surface-modifying agents include, for example,carboxylic acids, sulfonic acids, phosphonic acids, silanes, phosphates,and combinations thereof. Useful carboxylic acids include, for example,long chain aliphatic acids including octanoic acid, oleic acid, andcombinations thereof. Representative examples of polar modifying agentshaving carboxylic acid functionality include CH₃O(CH₂CH₂O)₂CH₂CO₂H,2-(2-methoxyethoxy)acetic acid, and mono(polyethylene glycol) succinate.Representative examples of nonpolar surface-modifying agents havingcarboxylic acid functionality include octanoic acid, dodecanoic acid,and oleic acid.

Exemplary useful silanes include organosilanes, for example,octyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane,3-mercaptopropyltrimethoxysilane, n-octyltriethoxysilane,phenyltriethoxysilane, p-tolyltriethoxysilane, vinyltrimethoxysilane,and combinations thereof.

Exemplary useful non-silane surface-modifying agents capable ofassociating with organic components of the composition include acrylicacid, methacrylic acid, beta-carboxyethyl acrylate,mono-2-(methacryloxyethyl) succinate, and combinations thereof. A usefulsurface-modifying agent that imparts both polar character and reactivityto the particles is mono-(methacryloxypolyethyleneglycol) succinate.

Nanoparticles can be surface modified using a variety of methodsincluding, e.g., adding a surface-modifying agent to nanoparticles(e.g., in the form of a powder or an aqueous sol) and allowing thesurface-modifying agent to react with the nanoparticles. A co-solventcan be added to the composition to increase the compatibility (e.g.,solubility or miscibility) of the surface-modifying agent and/or surfacemodified particles with the aqueous mixture.

The surface-modified nanoparticles may be intimately mixed with acurable binder precursor that may be subsequently processed prior tocuring. The choice of binder precursor is not critical so long as it isnot reactive under ambient conditions with the surface-modifiednanoparticles. Exemplary binder precursors include, but are not limitedto, polymerizable materials such as free-radically polymerizablemonomers and oligomers such as acrylates, methacrylates, allyliccompounds, vinyl ethers, vinyl esters, and the like; epoxy resins; alkydresins; phenolic resins; cyanate esters; melamine andmelamine-formaldehyde resins; polyurethane resins, and mixtures thereof.Desirably, binder precursors comprise acrylates and/or methacrylates.

The binder precursor may include a catalyst or other curative in orderto facilitate cure. Such catalysts and other curatives will depend onthe nature of the binder precursor and may include those well known inthe curing art, for example, thermal free radical initiators, such asperoxides and azo compounds, photoinitiators, photocatalysts, aminehardeners, mercaptans, etc.

The binder precursor may be cured to form a binder by application ofenergy such as heat or actinic radiation (e.g., ultraviolet light andelectron beam radiation), or through addition of a catalyst or curative.Desirably, in the case of free-radically polymerizable binderprecursors, a photoinitiator is present in the binder precursor and themixture is irradiated with ultraviolet actinic radiation from a lamp,desirably in an inert atmosphere such as nitrogen. The use of actinicradiation to cure the binder precursor allows a high degree offlexibility in the choice of protecting groups.

When used, the amount of actinic radiation energy used for curingdepends upon a number of factors, such as the amount and the type ofreactants involved, the energy source, web speed, the distance from theenergy source, and the thickness of the material to be cured. As generalguidelines, actinic radiation typically involves a total energy exposurefrom about 0.1 to about 10 Joules per square centimeter, and electronbeam radiation typically involves a total energy exposure in the rangefrom less than 1 megarad to 100 megarads or more, desirably 1 to 10megarads. Exposure times may be from less than about 1 second up to 10minutes or more.

Commercially available free-radical generating photoinitiators suitablefor the invention include, but are not limited to, benzophenone, benzoinether, and acylphosphine photoinitiators such as those sold under thetrade designations IRGACURE and DAROCUR from Ciba-Geigy Corp. (Ardsley,N.Y.). The amount of photoinitiator(s) used typically varies between 0.1and 15 weight percent, desirably between 0.5 and 7 weight percent, basedon the total weight of the binder precursor.

Co-initiators and amine synergists can be included in order to improvecuring rate. Examples of such include isopropylthioxanthone, ethyl4-(dimethylamino)benzoate, 2-ethylhexyl dimethylaminobenzoate, anddimethylaminoethyl methacrylate.

The volume ratio of surface-modified nanoparticles to binder precursormay range from 1:99 up to 70:30, desirably from 5:95 up to 55:45, andmore desirably from 10:90 up to 40:60.

For applications in which transparency is important, nanoparticlespresent in the binder precursor and/or binder desirably have a smallparticle size (e.g., <40 nm) to minimize the effects of lightscattering.

Those skilled in the art will also appreciate that, depending on theapplication, the binder and its precursor can contain other optionaladjuvants, such as surfactants, antistatic agents (e.g., conductivepolymers), leveling agents, thermal initiators, photosensitizers, UVabsorbers, stabilizers, antioxidants, fillers, lubricants, pigments,dyes, plasticizers, suspending agents, and the like.

Articles

As illustrated in FIG. 1, a composite article 100 may comprise ananocomposite layer 10 containing Ti/Sb mixed oxide nanoparticles 30dispersed in a binder 40, and supported on a substrate 20, wherein atleast a portion of the Ti/Sb mixed oxide nanoparticles contain arutile-like crystalline phase.

The substrate may be virtually any solid material. Non-limiting examplesof such substrates include glass (including electronic displays),quartz, transparent or translucent ceramics, wood, metal, paintedsurfaces including painted metals, and thermoset and thermoplasticmaterials such as acrylic polymers (e.g., polymethyl methacrylate),polycarbonates, polyurethanes, polystyrene, styrene copolymers, such asacrylonitrile-butadiene-styrene copolymer and acrylonitrile-styrenecopolymer, cellulose esters (e.g., cellulose acetate, cellulosediacetate, cellulose triacetate, and cellulose acetate-butyratecopolymer), polyvinyl chloride, polyolefins (e.g., polyethylene andpolypropylene), polyamides, polyimides, phenolic resins, epoxy resins,polyphenylene oxide, and polyesters (e.g., polyethylene terephthalate).Thermoplastic materials may contain fillers and other adjuvants.

Desirably the substrate is glass or a thermoplastic polymer film.Substrates may be either opaque or transparent depending on theapplication.

Nanocomposite layer 10 may be prepared by coating a compositioncomprising nanoparticles 30 and a binder precursor onto substrate 20,and curing the binder precursor. Coating may be accomplished byvirtually any known coating means that does not chemically or physicallyalter properties of the binder precursor. Exemplary coating methodsinclude, for example, spin coating, knife coating, wire coating, floodcoating, padding, spraying, exhaustion, dipping, roll coating, foamtechniques, and the like.

The thickness of the mixture of binder precursor and nanoparticle layerthat is applied will depend on the particular primary substrate andapplication. For protective coatings, the thickness of the resultantcured nanocomposite layer is desirably in the range of from about 1nanometers up to about 50 micrometers or even thicker, more desirablyfrom about from about 0.5 micrometers to about 10 micrometers, and moredesirably from about from about 3 micrometers to about 6 micrometers.Thicker nanocomposite layers may lead to crazing and other defects overtime; however, thinner layers often do not provide enough surfacematerial to be scratch resistant.

When present as a coating on transparent or translucent substrates, theingredients in the nanocomposite layer are desirably chosen so that ithas a refractive index close to that of the substrate. This can helpreduce the likelihood of Moiré patterns or other visible interferencefringes.

Method of Making Ti/Sb Mixed Oxide Nanoparticles and Colloids

Ti/Sb mixed oxide nanoparticles are prepared by combining an aqueoustitania precursor with an aqueous antimony oxide precursor.

As intimate mixing of titanium and antimony atoms in the crystal latticeis highly desirable, aqueous antimony oxide precursors are desirablymolecular species (i.e., species having a single antimony atom) orloosely associated species that dissociate under reaction conditions.Any titania or antimony oxide precursors meeting this requirement may beused.

Exemplary aqueous titania precursors include the reaction products ofhydrogen peroxide with titanium alkoxides. Exemplary alkoxides includeas 1-butoxide, 2-ethylhexoxide, 2-methoxy-1-ethoxide, linear andbranched alkoxides (such as ethoxide, 1-propoxide, 2-propoxide,2-butoxide, iso-butoxide, tert-butoxide, hexoxide, and the like). Two ormore of the same or different organic ligands may be attached to thetitanium. Desirably, the aqueous titania precursor is a reaction productof a titanium alkoxide with hydrogen peroxide.

Exemplary aqueous antimony oxide precursors include the reactionproducts of antimony alkoxides with hydrogen peroxide and HSb(OH)₆.Exemplary alkoxides include 1-butoxide, 2-ethylhexoxide,2-methoxy-1-ethoxide, linear and branched alkoxides (such as ethoxide,1-propoxide, 2-propoxide, 2-butoxide, isobutoxide, tert-butoxide,hexoxide, and the like). Two or more of the same or different organicligands may be attached to the antimony.

The aqueous titania and antimony oxide precursors are combined withmixing and simultaneously, or sequentially, are subjected to conditionswhereby they form a mixed oxide. The amount of each precursor employedis determined based on the stoichiometric quantity required to prepareTi/Sb mixed oxide nanoparticles of the invention as described above.Additionally, aqueous metallic oxide precursors may be mixed with theaqueous titania and antimony oxide precursors, if desired.

After mixing the aqueous titania and antimony oxide precursors, themixture is typically subjected to heat and pressure. In someembodiments, this may be accomplished by means of a pressure vessel suchas a stirred or non-stirred pressure reactor, commercially availablefrom Parr Instruments Co. (Moline, Ill.). The vessel should be capableof withstanding pressure and capable of sealing. The vessel containingthe mixture is sealed, and the solution is heated to a temperaturesatisfactory to drive the hydrolysis and condensation of the reactants.Typically, the vessel is heated at a rate of about 5° C./minute untilthe desired temperature is reached. Suitable pressures are governed bythe temperature and the vessel used to heat the reaction mixture.Generally, the desired temperature is greater than 120° C. and less than300° C. Desirably, the temperature is between about 150° C. and about200° C. Heating the solution within the closed vessel creates pressure.The pressure within the vessel is typically between 18 atmospheres to 40atmospheres. Typically, the solution is heated for up to 5 hours toensure complete hydrolysis although shorter reaction times can beeffective. The length of the heating time is determined by the timenecessary to achieve the desired temperature of the bulk. Once thistemperature is achieved, the reaction is typically over virtuallyinstantaneously. Additional time at this temperature typically leads toincreasing crystallite sizes, which usually trends with decreasedcolloidal stability of the nanoparticles. Desirably, the ensembleaverage rutile-like crystallite size of Ti/Sb mixed oxide nanoparticlesis less than about 20 nm, more desirably less than about 15 nanometers.

After heating and subsequent cooling to room temperature, the mixedmetal oxide particles are typically observed as a slurry of a solidprecipitate (i.e., agglomerated Ti/Sb mixed oxide nanoparticles) in theaqueous vehicle. The particles may be separated from the liquid bytransferring the slurry into centrifuge bottles, centrifuging theslurry, and decanting the supernate. Other methods of separating themixed metal oxide particles from the reaction mixture are possible suchas filtration, sedimentation, or flushing.

Alternatively, any unwanted components of the reaction mixture may beremoved by evaporation or by selective distillation. At this point, themetal oxide particles may, optionally, be dried.

Ti/Sb mixed oxide nanoparticles can also be prepared using a stirredtube reactor (i.e., STR). Stirred tube reactors typically have a motordriven shaft that is coaxially positioned along the length of a heatedtube. The shaft has multiple paddles mounted to it that provide mixingand heat transfer of the reaction mixture. Stirred tube reactors arewell known in the art. One particular STR design is described in Example15.

One embodiment of a process for preparing colloidal dispersions of Ti/Sbmixed oxide nanoparticles of the invention using an STR is outlined inFIG. 2. A reservoir 210 contains an aqueous mixture of a titaniaprecursor and an antimony oxide precursor having a solids content of 1-2weight percent. Pump 220 feeds the aqueous mixture into STR 230 that isheated to around 180 C to 220° C. in order to provide the heat necessaryto set off the hydrothermal reaction that forms the nanoparticles.Desirably, pump 220 is capable of maintaining a substantially even flowrate (e.g., a diaphragm pump). Exemplary stirred tube reactors aredescribed in U.S. Pat. No. 5,644,007 (Davidson et al.); U.S. Pat. No.5,814,278 (Maistrovich et al.); U.S. Pat. No. 4,770,777 (Steadly); andU.S. Pat. No. 6,448,353 B1 (Nelson et al.), each of which isincorporated herein by reference.

In order to avoid pulsations due to the pump, which may lead tobroadening of the particle size distribution, and to assist in applyingsurface functionalizing agent to the nanoparticles, a pulse dampener 240is desirably disposed between pump 220 and STR 230. Hydraulic pulsedampeners are well known in the art. Exemplary pulse dampeners includeclosed-end pipes and are described in U.S. Pat. Nos. 5,816,291 and2,504,424, each incorporated herein by reference. Desirably the pulsedampener comprises a closed-end stand pipe.

One particularly useful embodiment of a pulse dampener is depicted inFIG. 3. Pulse dampener 300 contains a pressurized fluid 315, andconsists of a length of pipe 310 having a cap 320 and an air cavity 325at the uppermost end of the pipe, and a pressurized fluid inlet 330 atthe lowermost end of the pipe. Transfer pipe 340 is perpendicularlyjoined to pipe 310. Transfer pipe 340 is joined to back pressure valve370, which has an outlet pipe 380. Pipes 310, 340 and 380 are connectedsuch that fluid travels from the inlet pipe to the outlet pipe withoutloss of material. When used in practice of this embodiment of theinvention, pressurized fluid emerges from outlet pipe 380 and enters theSTR. Thus, a diaphragm pump may on its forward stroke push a liquid intopressurized fluid inlet 330 causing air cavity 325 to shrink in volumeas the air compresses. On the return stroke as the diaphragm pumprefills for the next delivery, the compressed air acts as amini-compression feed chamber and returns liquid to the fluid stream.The cycle repeats over and over as the pump operates, thereby smoothingpressure pulses of the fluid being pumped.

Typical residence times of the aqueous mixture in STR 230 are 10-20minutes. After leaving STR 230, the heated mixture passes through a heatexchanger 250 to cool the mixture down before collection. Optionally, asecond pump 260 may add a surface functionalizing agent in reservoir 290to the heated mixture just prior to entering the heat exchanger in orderto treat the surface of the particles to prevent agglomeration. Aback-pressure regulator valve 270 is positioned after the heat exchangerand controls the pressure of STR 230 to make sure that the water staysin a liquid state. Typical pressures in the STR are around 250 to 350pounds per square inch (1.7 to 2.4 megaPascals). The STR providesinternal mixing, which facilitates efficient heat transfer. In addition,the mixing action of the STR provides plug flow conditions inside thereactor.

After hydrothermal processing, the colloidal dispersion of Ti/Sb mixedoxide nanoparticles may contain outlier (i.e., excessively large)particles. As a result, the aqueous colloidal dispersion coming out ofthe STR may not be optically transparent. These outlier particles may beremoved by centrifugation thereby improving the clarity of the colloidaldispersion and narrowing the particle size distribution.

The colloidal dispersion may be used in that form or solvent (e.g.,water) may be replaced with an organic solvent or a solution containingan organic solvent and a dispersing aid to form a slurry using methodswell known in the art. Solvents used in the present invention may bechosen based on volatility and compatibility with any binder precursorthat may be used in combination with the nanoparticles. Typical organicsolvents include C₆-C₁₂ aliphatic compounds, aromatic compounds,alcohols, ethers, esters, and/or ketones. Exemplary aliphatic solventsinclude cyclohexane, heptane, toluene, xylene, 2-butanone, or4-methyl-2-pentanone, 1-methoxy-2-propanol, and the like.1-Methoxy-2-propanol is especially desirable.

Ti/Sb mixed oxide nanoparticles of the present invention may beadvantageously combined with at least one dispersing aid that attachesan organic moiety, desirably through at least one covalent bond, to thesurface of the metal oxide particles. Typical dispersing aids includealkoxysilanes such as alkyltrialkoxysilanes, organic acids such ascarboxylic acids, alcohols, polyethylene glycols, mono- or di-esters offatty acids, polyethylene oxide and polypropylene oxide, alkoxylatedphosphonic acids and their esters, and combinations thereof.

Desirably, dispersing aids include alkoxysilanes, desirablyoctyltriethoxysilane, octadecyltrimethoxysilane,hexadecyltrimethoxysilane, carboxylic acids, and combinations thereof.

Other suitable dispersing agents include stearic acid, oleic acid, andKEN-REACT Coupling Agent KR TTS, commercially available from KenrichPetrochemicals (Bayonne, N.J.). Dispersing aids that are coupling agentsmay be used. A coupling agent is a dispersing aid with two functionalgroups. Suitable coupling agents include methacrylic acid, glycine,glycolic acid, mercaptoacetic acid, methacryloyloxyethyl acetoacetate,allyl acetoacetate, 3-acryloxypropyltrimethoxysilane,3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane,3-glycidoxypropyltrimethoxysilane, 7-octen-1-yltrimethoxysilane, andallyl triethoxysilane.

After the addition of the dispersing aid, the colloidal dispersiontypically has a solids content in the range of from about 1 to about 2weight percent, although higher and lower solids contents may also beemployed. The colloidal dispersion is then stirred, preferably withheating at temperatures greater than 60° C. and less than about 95° C.,until the surface of the colloidally-dispersed particles issubstantially coated and/or reacted with the dispersing aid. Thecolloidal dispersion may be concentrated to give a colloidal dispersionhaving a solids content in the range of from about 2 to about 20 weightpercent, desirably from about 5 to about 10 weight percent. Thecolloidal dispersion typically has a ratio of dispersing agent to metaloxide of about 0.1 to 6.0 millimole/gram, desirably 0.2 to 2.0millimole/gram.

An amount of water (neutral, acidic, or alkaline) may then be added insufficient amount to remove any remaining hydrolyzable groups andfurther condense dispersing agents to the particle surface. For thepurpose of the present invention, base hydrolysis was found to beparticularly advantageous for hydrolysis of the alkoxyorganosilane andcondensation onto the particle surface.

An optional step involves the removal of high boiling point by-productsfrom the stable colloidal dispersion, whereby the stable colloidaldispersion is concentrated to a syrup by heat or vacuum drying. If thestable colloidal dispersion comprises a polar liquid, the crystallinenanoparticles are weakly flocculated by the addition of a non-polarliquid. If the stable colloidal dispersion comprises a non-polar liquid,the crystalline nanoparticles are weakly flocculated by the addition ofa polar liquid. The flocculated nanoparticles are typically isolated bycentrifugation and then washed by re-suspension in one of theflocculating liquids and separated by centrifugation. The precipitatemay be dried to form a powder, or the precipitate may be dispersed in anorganic liquid or solvent to form a colloid.

Colloids of the present invention are stable dispersions as measured bycentrifuging the colloid samples at 2500 rpm for 10 minutes. Colloids(or sols), if substantially free of sediment after centrifugation, aresaid to be stable dispersions.

The invention will now be described further by way of the followingexamples.

EXAMPLES

Materials employed in the examples that follow may be obtained fromgeneral commercial chemical vendors such as Aldrich Chemical Co.(Milwaukee, Wis.) unless otherwise indicated.

Test Methods Used in the Examples

Particle Size

Particle Size was determined by Photon Correlation Spectroscopicanalysis using a Coulter N4 Submicron Particle Analyzer, commerciallyavailable from Coulter Corp. (Miami, Fla.).

Crystalline Phase

X-ray diffraction analysis (i.e., XRD) was used to determine thecrystalline phase. Data were collected using a Philips verticaldiffractometer, commercially available from Philips ElectronicInstruments Co. (Mahwah, N.J.). The diffractometer was fitted withvariable entrance slits, fixed 0.2 degree receiving slit, graphitediffracted beam monochromator, and proportional detector for registry ofthe scattered radiation. A sealed copper target X-ray source was used atgenerator settings of 45 kV and 35 mA. Each sample was prepared as anethanol slurry on a glass substrate. Survey step scans were conductedfrom 5 to 80 degrees (20) using a 0.04 degree step interval and 4 secondcounting time. Identification of the crystalline phases present wasachieved by comparison (as described by H. P. Klug and L. E. Alexanderin “X-Ray Diffraction Procedures for Polycrystalline and AmorphousMaterials”, John Wiley & Sons, New York (1954)) of the observeddiffraction maxima to the patterns present in the International Centrefor Diffraction Data powder data file (International Centre forDiffraction Data, 12 Campus Boulevard, Newton Square, Pa.).

Intermediates Used in the Examples

Peroxy Titanic Acid

A 2-liter flask was charged with 848 g deionized water, 85 g of 30weight percent hydrogen peroxide, commercially available from FisherScientific (Pittsburgh, Pa.) and 32 g of 0.33 M aqueous ammoniumhydroxide. The stirred contents of the flask were cooled to 10° C. in acold-water bath, and 35.6 g titanium tetraisopropoxide, commerciallyavailable from Gelest, Inc. (Tullytown, Pa.) was added slowly over 3minutes resulting in an orange-yellow precipitate and the gentleevolution of gas. The slurry was allowed to slowly warm to roomtemperature over 6 hours over which time the precipitate was fullydigested to give a yellow, pourable liquid composed of peroxy titanicacid in water (theoretical yield was 1 weight percent TiO₂).

Antimony Hydrogen Peroxide Solution

A 1-liter flask was charged with 469 g deionized water and 21 g of 30weight percent hydrogen peroxide. The stirred contents were cooled to 5°C. in an ice bath, and 10.5 g antimony tri-n-butoxide was added slowlyover 3 minutes resulting in a white precipitate. The slurry was allowedto slowly warm to room temperature over 6 hours during which time theprecipitate was fully digested to give a clear colorless solution(theoretical yield was 1 weight percent Sb₂O₅).

Preparation of Colloidal HSb(OH)₆

A 0.5-liter flask was charged with 297 g deionized water, 20 g AMBERLITEIR-120 (plus) ion-exchange resin, and 4.9 g potassiumhexahydroxyantimonate. The resultant slurry was allowed to mix 14 hoursand subsequently heated to 65° C. for 1 hour to form a stable white sol.The sol was cooled to room temperature and filtered on a C-grade glassfrit to give an aqueous white colloid of HSb(OH)₆ with a measured pH of3 (theoretical yield was 1 weight percent Sb₂O₅).

Examples 1-13 and Comparative Examples A-C

Examples 1-13 and Comparative Examples A-C were generated according tothe following general procedure, with modifications to amounts ofingredients as indicated in Table 1, describes the preparation of anaqueous colloid containing Ti/Sb mixed oxide nanoparticles having arutile-like crystalline phase.

A 2-liter pressure reactor, commercially available from PressureProducts Industries, Inc. (Warminster, Pa.) was charged with about 1200g of a mixture of peroxy titanic acid and colloidal HSb(OH)₆ in a weightratio as indicated in Table 1. The reactor was heated to 180° C. for 3hours. The reactor was allowed to cool slowly to room temperature over12 hours. The resultant transparent colloid was filtered through a GF/Bfilter (glass fiber filter, 1.0 micrometer pore size), commerciallyavailable from Whatman, Inc. (Clifton, N.J.).

The results show that nanoparticles having rutile-like phases wereobtained for compositions of Ti/Sb mixed oxides having a theoreticalSb₂O₅ content greater than 10 weight percent, but less than 100 weightpercent. TABLE 1 Powder X-ray Diffraction Powder X-ray DiffractionDynamic Light Weight Relative Intensities Crystalline Sizes (nm) LatticeParameters Scattering^(a) Weight Percent Ratio of Sb₂O₅. Sb₂O₅. AnataseRutile Solution Particle Example Sb₂O₅ Sb/Ti Anatase Rutile 4H₂O AnataseRutile 4H₂O a c a c size (nm) Comparative 0 0.00 100 2 0 19.5* 0.0 0.03.796 9.528 — — 1000 Example A Comparative 5 0.07 100 1 0 24.5 0.0 0.03.802 9.541 — —  278 Example B  1 10 0.14 100 14 0 19.0 14.0 0.0 3.8009.522 4.610 2.974  233  2 15 0.22 19 100 0 13.0 13.5 0.0 3.797 9.5624.623 2.987  173  3 20 0.31 3 100 0 <5 12*  0.0 — — 4.628 2.990  42*  425 0.42 0 100 0 0.0 10.5 0.0 — — 4.633 2.997  51*  5 30 0.54 0 100 0 0.010.0 0.0 — — 4.639 2.998   6  6 35 0.68 0 100 0 0.0 9.0 0.0 — — 4.6383.010  32  7 40 0.84 0 100 0 0.0 9.8* 0.0 — — 4.649 2.997  30  8 45 1.030 100 0 0.0 10.0 0.0 — — 4.657 3.012   3  9 50 1.26 0 100 0 0.0 10.3*0.0 — — 4.657 3.001  28 10 60 1.88 0 100 0 0.0 11.5 0.0 — — 4.659 3.017 47 11 70 2.93 0 100 0 0.0 12.5 0.0 — — 4.664 3.006  166 12 80 5.02 0 71100 0.0 11.5 20.0 — — 4.666 3.025   6 13 90 11.30 0 12 100 0.0 12.0 17.5— — 4.658 3.018  105 Comparative 100 N/a 0 0 100 0.0 0.0 18.5 — — — — 30 Example CIn Table 1,*indicates the value is the numerical average of two separatemeasurements.

Example 14

This example describes the preparation of an aqueous colloid of Ti/Sbmixed oxide nanoparticles having a rutile-like crystalline phase.

A 2-liter pressure reactor was charged with 1369 g of peroxy titanicacid and 342 g colloidal HSb(OH)₆ (weight ratio was 80 parts titaniumdioxide to 20 parts antimony oxide). The reactor was heated to 180° C.for 2 hours. The pressure in the reactor reached 300 pounds per squareinch (2.07 megaPascals). The reactor was cooled quickly to 75° C. bypacking the outside of the reactor with dry ice. The reaction produced atransparent colloid with a slight blue hue and a measured particle sizeof 31.9 nanometers with a standard deviation of 6.4 nanometers. Aportion (i.e., 5 mL) of the colloid was dried in a 100° C. oven and theresultant powder was analyzed by XRD which showed a rutile-like peakwith 100 percent relative intensity having a 20.5 nanometers crystallitesize and a 49 percent relative intensity anatase peak having a 15.0nanometers crystallite size. There was no evidence of a separateantimony oxide phase, instead the observed diffraction maxima for therutile-like phase were slightly shifted from rutile itself, indicatingthe antimony atoms were distributed throughout the lattice structure.

Example 15

This example shows the use of a stirred tubular reactor to prepare Ti/Sbaccording to one embodiment of the invention.

Colloidal HSb(OH)₆ was added to peroxy titanic acid such that acalculated weight ratio of TiO₂ to Sb₂O₅ was 80/20 obtained. Sufficientconcentrated ammonium hydroxide was added to the mixture in order toraise the pH to about 7, which made the precursor stable and preventedgelation. The mixture formed an intermediate peroxy complex that wasallowed to digest over 3 hours to form a clear orange solution of mixedmetal peroxy complex (1 percent TiO₂/Sb₂O₅ by weight).

The mixture was injected in to a 316 stainless steel 2-liter stirredtube reactor operated at a heater temperature of 204° C. and a residencetime of 11.1 minutes. The length of the STR was 60 inches and the insidediameter was 2 inches to give an L/D ratio of 30. The throughput was 180grams per minute, and the stirring motor speed was 120 revolutions perminute. The system pressure was 300 pounds per square inch (2.1megapascals). The temperature at the output of the reactor was 190° C.

The mixture was pumped through the reactor using a diaphragm pump (ModelNo. EK-1) commercially available from American Lewa, Inc. (Holliston,Mass.) having a pulse dampener consisting of an air cavity made from anend-capped length of 10 inch ½″ OD stainless steel pipe, and a backpressure valve arranged as depicted in FIG. 3 contiguously situatedbetween the pump and the inlet to the STR. The output mixture from theSTR was immediately passed through a heat exchanger to rapidly cool themixture to about 75-80° C. The particle size of the resultant colloidaldispersion was determined using a CHDF 2000 particle analyzer obtainedfrom Matec Applied Sciences, Inc. (Northborough, Mass.). The weightaverage particle size was 123 nanometers.

This dispersion was centrifuged using a CARR POWERFUGE PILOT gravitycentrifuge available from Kendro Laboratory Products (Franklin, Mass.)using a speed setting of 10 (corresponding to a G-Force of 20,308)resulting in a transparent colloidal dispersion of Ti/Sb mixed oxidenanoparticles, exhibiting a rutile-like crystalline phase, having aweight average particle size of 64 nanometers and a narrow sizedistribution.

Example 16

This example shows the preparation of a composite article employingcolloidal surface modified Ti/Sb mixed oxide nanoparticles having arutile-like crystalline phase.

An 8-ounce (237 milliliters) glass jar was charged with 100 grams ofantimony doped titanium oxide colloid (as prepared in Example 3) and 600milligrams SILQUEST A1230 (a silane coupling agent commerciallyavailable from Witco Corp. of Endicott, N.Y.). The transparent colloidwas placed in an 80 C oven for 16 hours, then cooled to roomtemperature. The colloid was transferred to a flask and reduced down to3 grams utilizing a rotary evaporator. 1-Methoxy-2-propanol (18 grams,commercially available from Aldrich of Milwaukee, Wis.) was added to thecolloid and the mixture was reduced to 7 grams utilizing a rotaryevaporator. 1-Methoxy-2-propanol (12 grams) was added to the colloid andthe mixture was reduced utilizing a rotary evaporator to give finalcolloid with 8.1 weight percent metal oxide.

This colloid was mixed with 1.85 grams of a mixture of 30 weight percentSR 295 (trade designation for pentaerythritol tetraacrylate), 30 weightpercent SR 506 (trade designation for isobornyl acrylate), and 40 weightpercent SR 238 (trade designation for 1,6-hexanediol diacrylate) allcommercially available from Sartomer Company, Inc. (Exton, Pa.).Tris(N-nitroso-N-phenylhydroxyl-aminato)aluminum (2 milligrams)available from First Chemical Corp. (Pascagoula, Miss.) was added to themixture, which was then reduced utilizing a rotary evaporator to 3.83grams. Thermogravimetric analysis of the resin indicated 22.65%inorganic solids in the resin. 2,4,6-Trimethylbenzoyl-diphenyl-phosphineoxide liquid photoinitiator commercially available from BASF Corp.(Mount Olive, N.J.) under the trade designation LUCIRIN LR 8893, wasadded at 1 percent to the resin that was then bar coated at 0.5 milsthickness onto a 0.125 inch polymethyl methacrylate sheeting.

The coated sample was cured by passing the coated sample through aFusion UV Systems UV processor (VPS-6 power supply, EPIQ 6000 irradiatorobtained from Fusion UV Systems, Corp. (Rockville, Md.) that wasequipped with a “D”-bulb on full power (600 W/in) and operating at aline speed of 40 feet per minute (12.2 meters per minute).

The resultant cured coated film had a measured refractive index of1.569.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention. It therefore should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth above, but is to be controlled by the limitationsset forth in the claims and equivalents thereof.

1. A nanocomposite precursor comprising a plurality of nanoparticleshomogeneously dispersed in an organic binder precursor, wherein thenanoparticles comprise Ti/Sb mixed oxide nanoparticles containing arutile-like crystalline phase, wherein the ensemble average rutile-likecrystalline phase content of the Ti/Sb mixed oxide nanoparticles is atleast 20 weight percent, and wherein the weight ratio of antimony totitanium in the Ti/Sb mixed oxide nanoparticles is in a range of from atleast 0.42 up to and including 2.93.
 2. The nanocomposite precursor ofclaim 1, wherein the ensemble average nanoparticle size is less thanabout 100 nanometers.
 3. The nanocomposite precursor of claim 1, whereinthe ensemble average nanoparticle size is less than about 40 nanometers.4. The nanocomposite precursor of claim 1, wherein the ensemble averagerutile-like crystalline phase content of Ti/Sb mixed oxide nanoparticlesis at least about 40 weight percent.
 5. The nanocomposite precursor ofclaim 1, wherein the ensemble average rutile-like crystalline phasecontent of Ti/Sb mixed oxide nanoparticles is at least about 60 weightpercent.
 6. The nanocomposite precursor of claim 1, wherein the ensembleaverage rutile-like crystalline phase content of Ti/Sb mixed oxidenanoparticles is at least about 80 weight percent.
 7. The nanocompositeprecursor of claim 1, wherein substantially all of the Ti/Sb mixed oxidenanoparticles contain a rutile-like crystalline phase.
 8. Thenanocomposite precursor of claim 1, wherein the nanoparticles have atleast one organic moiety bound to the nanoparticle surface.
 9. Thenanocomposite precursor of claim 1, wherein the binder precursorcomprises a polymerizable material.
 10. The nanocomposite precursor ofclaim 9, wherein the polymerizable material comprises an acrylatemonomer or oligomer.
 11. The nanocomposite precursor of claim 9, whereinthe binder precursor further comprises a photoinitiator orphotocatalyst.
 12. A nanocomposite comprising a plurality ofnanoparticles dispersed in an organic binder, wherein the nanoparticlescomprise Ti/Sb mixed oxide nanoparticles containing a rutile-likecrystalline phase, wherein the ensemble average rutile-like crystallinephase content of the Ti/Sb mixed oxide nanoparticles is at least 20weight percent, and wherein the weight ratio of antimony to titanium inthe Ti/Sb mixed oxide nanoparticles is in a range of from at least 0.42up to and including 2.93.
 13. The nanocomposite of claim 12, wherein theensemble average nanoparticle size is less than about 100 nanometers.14. The nanocomposite of claim 12, wherein the ensemble averagenanoparticle size is less than about 40 nanometers.
 15. Thenanocomposite of claim 12, wherein the ensemble average rutile-likecrystalline phase content of Ti/Sb mixed oxide nanoparticles is at leastabout 40 weight percent.
 16. The nanocomposite of claim 12, wherein theensemble average rutile-like crystalline phase content of Ti/Sb mixedoxide nanoparticles is at least about 60 weight percent.
 17. Thenanocomposite of claim 12, wherein the ensemble average rutile-likecrystalline phase content of Ti/Sb mixed oxide nanoparticles is at leastabout 80 weight percent.
 18. The nanocomposite of claim 12, whereinsubstantially all of the Ti/Sb mixed oxide nanoparticles contain arutile-like crystalline phase.
 19. The nanocomposite of claim 12,wherein the nanoparticles have at least one organic moiety bound to thenanoparticle surface.
 20. The nanocomposite of claim 12, whereinnanoparticles are present in an amount of at least 30 weight percent ofthe nanocomposite.
 21. The nanocomposite of claim 12, wherein the bindercomprises a polymerized acrylate monomer.
 22. The nanocomposite of claim12, wherein the binder further comprises a photoinitiator orphotocatalyst.